Summary of Significant Accounting Policies Construction in Progress (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Construction in Progress [Line Items]
Internal direct construction costs capitalized related to development of properties and land holdings	$ 4,700	$ 4,000	$ 3,900
Interest Costs Capitalized	2,600	2,000	10,400
Salaries including bonuses and benefits, capitalized during the period	4,669	4,034	3,853
Development [Member]
Construction in Progress [Line Items]
Salaries including bonuses and benefits, capitalized during the period	57	0	2,331
Redevelopment [Member]
Construction in Progress [Line Items]
Salaries including bonuses and benefits, capitalized during the period	353	0	127
Tenant Improvements [Member]
Construction in Progress [Line Items]
Salaries including bonuses and benefits, capitalized during the period	$ 4,259	$ 4,034	$ 1,395